The monitoring of electrically charged particles is required in many technologies. In devices as varied as mass spectrometers, ion implanters, and scanning electron microscopes, electrically charged particles are projected along a path and then used to achieve a desired result. In particle colliders, such as the Relativistic Heavy Ion Collider at Brookhaven National Laboratory in Long Island, New York, electrically charged particles are projected along a path for the purpose of studying the characteristics of the particles. Accordingly, there is a need to monitor electrically charged particles as they travel along a path without significantly altering the energy, direction, velocity, charge, or state of the electrically charged particles.
An example of a particle detector is disclosed in U.S. Pat. No. 3,450,879 to Seppi et al. entitled "Dielectric-Type Charged Particle Detector". In this patent, the detector includes a thin dielectric in contact with a pair of electrodes wherein a voltage is applied to the dielectric through the electrodes resulting in a current that is proportional to the intensity of irradiation impinging on the dielectric. In U.S. Pat. No. 3,567,925 to Muga et al. entitled "An Improved Charged Particle Detector", a beam of charged particles passes through a thin scintillator film of the detector and then impinges upon a solid state surface barrier detector. Each of these devices requires that the charged particles impinge on a portion of the detector, and may result in an adverse change in the energy, direction, velocity, charge, or state of the electrically charged particles.
A system for detecting charged particles without destroying the charged particles is disclosed in U.S. Pat. No. 3,492,480 to Vogel entitled "System for the Detection Of Charged Particles". In this patent, a bunch of charged particles passes through sensor rings inducing a voltage across the terminals of a ringing circuit consisting of a capacitor and an inductor. This voltage excites oscillations in a ringing circuit with a linear buildup of oscillation amplitude. This system, however, may require synchronism between the pulses of electric charge from the charged particles and the frequency of the ringing circuit. For high sensitivity, this system may also require supercooling the resonating circuit or employment of resonators such as piezoelectric crystals.
An apparatus for monitoring the current comprised by a beam of charged particles such as a focused ion beam as used for ion implantation is disclosed in U.S. Pat. No. 3,857,090 to Chick entitled "Generation of Beams of Charged Particles". In this patent, the apparatus includes detector means that may comprise a toroidal coil or toroidal coil system surrounding the beam and producing an output voltage signal of magnitude in the order of millivolts. The detector means is responsive to the magnetic field of the beam and provides an output signal corresponding to the modulation of the strength of the magnetic field of the beam and therefore proportional to the beam current. Accordingly, this apparatus modulates the amplitude of the beam and therefore may not be adapted for monitoring individual charged particles or pulses of charged particles.
A system for scanning a charged particle beam, and monitoring and controlling of the source of the beam energy is disclosed in U.S. Pat. No. 4,687,936 to Mcintyre et el. entitled "In-Line Beam Scanning System". In this patent, the beam pulse amplitude is monitored by a toroid.
Notwithstanding the above mentioned devices for detecting beams of electrically charged particles, there continues to be a need for an apparatus and method for monitoring individual electrically charged particles and pulses of electrically charged particles without destroying the particles or significantly altering the energy, direction, velocity, charge, or state of the particles. In particular, there exists a need for an apparatus and method for monitoring individual charged particles and pulses of charged particles occurring at randomly spaced intervals in time.